Screen ETFs

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already mark read-only, non-destructive, closed-world, so the safety profile is covered. The description adds value beyond them: it warns this is an expensive full-universe read, notes request limits depend on connection/plan, advises building one precise screen to conserve allowance, reports evaluatedCount/matchCount, and states percentages are percentage points. That is substantial extra behavioral context, though it doesn't discuss latency or failure modes.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loaded with the core action and the sibling comparison, and each sentence conveys actionable information (routing rule, unit convention, cost warning). The long attribute enumeration is dense but purposeful; the only mild bloat is the full metric list repeating enum values.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given 24 optional parameters, a rich schema and an output schema, the description covers the essentials an agent needs: when to pick this tool, cost constraints, unit conventions, and the evaluatedCount/matchCount return signal. Remaining gaps (pagination, output field shapes) are handled by the output schema, so it is nearly complete for a tool of this complexity.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so every one of the 24 parameters is already documented in structured fields, which sets the baseline at 3. The description adds the percentage-point unit convention and a couple of example values, but most semantic weight is carried by the schema's own per-parameter descriptions (groupId AND/OR grouping, EXCLUDES semantics, includeSecondary venue handling).

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ("Screen the WHOLE ETF universe") and enumerates the metric families it can filter on, so the tool's scope is unmistakable. It explicitly distinguishes itself from search_etfs (full-universe evaluation vs. bounded candidate scan), letting an agent tell the two apart without opening a schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives an explicit routing rule: prefer this over search_etfs for "cheapest / largest / best performing / most liquid" questions, with the reason stated. The schema and description also point to get_etf_index_group and get_etf_filter_options for adjacent needs, covering the when-to-use and when-to-use-else paths.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.